1. Field of the Invention
The present invention relates to a light-emitting device, and more particularly, to an alternating current light emitting device and the fabrication method thereof.
2. Description of Related Art
Unlike the light emission principle of white light, the light emission principle of light emitting diodes (LEDs) involves applying electric current to light-emitting materials so as to produce light. Hence, LEDs are also known as cold light sources. LEDs have their own advantages, namely highly durable, longevity, light and compact, low power consumption, absence of harmful substances such as mercury, and so forth, thus the development of LED-based solid state lighting has become one of the crucial research targets for the global lighting industry as well as the semiconductor industry. Common applications of LEDs include white light illumination, indicator lights, vehicle signal and illuminating lights, flash lights, LED back-light modules, projector light sources, outdoor displays, and so forth.
White light devices, the most important lighting application, still require a patented fabrication process of Nichia fluorescent powder. In addition to the necessity of paying royalties, drawbacks of the patented Nichia process include the distribution ratio of fluorescent powder and the relatively high color temperature of white light arising from a coverage process that leads to shortened operating life and even high temperature-induced failure. Moreover, the prior art fails to provide good packaging control, making mass production more difficult.
Taiwanese Patent Application No. 093126201 discloses a light-emitting diode (LED) die structure having an alternating current circuit, comprising at least one alternating current micro-die LED module formed on a chip and composed of two opposite-polarity micro-die LEDs connected in parallel, so as to apply alternating current thereto, such that two micro-die LEDs can, working in turn, emit light during positive and negative half cycles of the AC waveform to overcome the drawback of the prior art, that is, DC-driven light emission occurs in the presence of forward current rather than reverse current, with a view to using alternating current as a power source to greatly promote application of LED elements.
In the foregoing patent, due to the plane array configuration adopted, each micro-die of a LED only emits light under forward or reverse bias within an alternating current cycle. In other words, at every single moment, a light-emitting area merely accounts for a half of the surface area of a chip, while the micro-dies associated with another half of the surface area of the chip are in an off state, resulting in a waste of the light-emitting area. Furthermore, it is necessary to double the current density in order to attain full-plane luminosity.
Further, a micro-die disclosed by the aforesaid patent has an isosceles, right-angle triangular shape with two legs approximately a mere 70 micrometers long each, causing difficulty in the fabrication process where it is necessary to reduce the size of the LEDs in order to meet the need for product miniaturization. Furthermore, since the aforesaid patent involves the use of patented Nichia fluorescent powder, the foregoing drawbacks of high color temperature and a hard-to-control packaging process still exist.
Therefore, there exists an urgent need to develop an innovative alternating current light-emitting device that not only solves the aforesaid drawbacks of the prior art, but also provides a full-scale light-emitting area for all-time, even light emission characterized by low color temperature and a relatively great overlapped range of color temperatures. The proposed alternating current light-emitting device does not use the patented Nichia fluorescent powder, thereby allowing the fabrication process to be carried out more smoothly and the mass production to be more controllable, and in consequence the industrial applicability of the proposed alternating current light-emitting device is enhanced.